Pressure vessel penetration techniques

ABSTRACT

Control line penetration of a nuclear reactor pressure vessel is achieved through the side of the vessel below the junction of the vessel main barrel portion and the reactor head. The control lines enter the pressure vessel in the form of a bundle of conduits at a point which is out of the main coolant flow path and the control lines are provided with disconnect means internally of the vessel.

United States Patent 1191 Bevilacqua et al.

PRESSURE VESSEL PENETRATION TECHNIQUES Inventors: Frank Bevilacqua,Windsor;

Malcolm D. Groves; Gennaro V. Notari, both of Simsbury, all of Conn.

Combustion Engineering, Inc., Windsor, Conn.

Filed: Dec. 23, 1971 Appl. No.: 211,369

Assignee:

US. Cl. 176/36 R, 176/87, 285/28 Int. Cl G2lc 7/16 Field of Search176/36 R, 78, 86 R, 87;

References Cited UNITED STATES PATENTS 3/1955 Pfau 285133 a a W l.

[ Oct. 29, 1974 3,346,459 10/1967 Prince et al 176/36 R 3,442,760 5/1969Rigg l76/65 x 3,548,077 12/1970 Talley 138/110 x 3,660,230 5/1972Bailey, Jr..'. 176 36 R FOREIGN PATENTS OR APPLICATIONS 1,171,822lO/l958 France .7. 176/36 R 91,371 8/1968 France 285/28 PrimaryExaminerHarvey E. Behrend [5 7] ABSTRACT Control line penetration of anuclear reactor pressure vessel is achieved through the side of thevessel below the junction of the vessel main barrel portion and thereactor head. The control lines enter the pressure vessel in the form ofa bundle of conduits at a point which is out of the main coolant flowpath and the control lines are provided with disconnect means internallyof the vessel.

14 Claims, 13 Drawing Figures PMENFEMWZQW sum m 7 3.844.883

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ACCUMULATOR PRIMARY SYSTEM PRESSURE VESSEL PENETRATION TECHNIQUESBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to nuclear reactors and particularly to reactorcontrol systems. More specifically, this invention is directed totechniques and apparatus for hydraulic control line penetration of areactor pressure vessel. Accordingly, the general objects of the presentinvention are to provide novel and improved methods and apparatus ofsuch character.

2. Description of the Prior Art In the operation of a nuclear reactor itis requisite that the position of absorber or moderator elements, alsoknown as control rods, with respect to the fuel assembly be constantlymonitored and controlled. In the prior art the control assemblies forthe absorber elements are typically in the form of cylinders whichextend out of the reactor through the pressure vessel head. Extension ofthe control assembly cylinders out through the vessel head has resultedin a cluttered head and has exposed the absorber position controldevices to the possibility of physical damage.

As a result of the extension out of the pressure vessel of the actuatorcylinders, it has previously been necessary to individually disconnectand disassemble the control devices prior to pressure vessel headremoval as is necessary for inspection and maintenance operations suchas refueling. This, in turn, has imposed a substantial economic penaltyon the reactor operator by increasing reactor down time during refuelingand other routine maintenance or inspection operations.

SUMMARY OF THE INVENTION The present invention overcomes the abovebriefly discussed and other disadvantages of the prior art by providinga novel and improved manner of penetrating a reactor pressure vesselwith hydraulic control lines. In accordance with the present inventionthe control lines, in the form of a bundle of tubes, penetrate the sideof the reactor vessel at a point below the junction of the main vesselportion and head. The penetration location is selected so as to be outof the main coolant flow path. In accordance with the preferredembodiments of the invention, internally of the pressure vessel thecontrol lines are positioned in the annulus between the reactor corebarrel and the pressure vessel internal wall as they are directedupwardly'into the area encompassed by the vessel head. Disconnectingmeans is provided in a location which is accessible with the headremoved whereby the control lines may be readily separated when the corebarrel is removed.

As will be obvious from the preceding description, in accordance withthe present invention there is no control line penetration of the vesselhead thus providing a clean" head which may be readily removed afterunbolting. Accordingly, the penetration in accordance with the inventionis located in a comparatively protected area whereby damage is lesslikely to occur.

BRIEF DESCRIPTION OF THE DRAWING The present invention may be betterunderstood and its numerous objects and advantages will become apparentto those skilled in the art by reference to'the accompanying drawingwherein like reference numerals the present invention;

refer to like elements in the several figures and in which:

FIG. 1 is a schematic view of a top actuated reactor control system inaccordance with the present invention; FIG. 2 is an enlarged view,partially in section, of the pressure vessel of the reactor of FIG. 1,FIG. 2 showing generally the placement of the fuel and control ele mentswithin the vessel;

FIG. 3 is a side elevation view, partially in section, of a firstembodiment of a control rod assembly in accordance with the presentinvention;

FIG. 3A is an enlarged view of a portion of a preferred embodiment ofthe control rod assembly of FIG. 3; I

F IG.- 3B is an enlarged view of cooperating portions of the top bufierand piston of the control rod assembly of FIG. 3;

FIG. 4 is-a side elevation view, partially in section, of a firstembodiment of a pressure vessel control line penetration technique andapparatus in accordance with the present invention;

FIG. 5 is an enlarged, cross-sectional view of the internal control linedisconnect assembly of the apparatus shown in FIG. 4;

FIG. 5A is an enlarged perspective view of a portion v of the disconnectassembly of FIG. 5;

FIG. 6 is a cross-sectional, sideelevation view of a second embodimentof a pressure vessel control line penetration technique and apparatus inaccordance with the present invention;

FIG. 7 is an enlarged, cross-sectional view of the internal control linedisconnect assembly of the apparatus shown in FIG. 6;

FIG. 8 is a cross-sectional, side elevation ,view of a third embodimentof a pressure vessel control line penetration technique and apparatus inaccordance with FIG.'9 is a cross-sectional, side elevation view of afourth embodiment of a pressure vessel control line penetrationtechnique and apparatus in accordance with the present invention; and

FIG. 10 is a cross-sectional, side elevation view of fuelassembly holddownscheme and apparatus in accordance with the invention. a

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIG. 1,the pressure vessel of a pressurized water reactor is indicatedgenerally at 10. Reactor vessel 10 provides a housing for the variouselements of a fission type nuclear reactor of the kind employed byutilities to heat a circulating coolant; the coolant thereafter beingrouted through the heat exchangers and other components of a steamgenerator and the steam thus provided being employed to drive a turbineand its associated electrical power generator. In FIG. 1 the steamgenerators and associated equipment have been labeled Primary System andare indicated generally at 12. The main circulating pump for the coolantis indicated at 14 and supplies, via conduit or cold leg 16, the coolantto pressure vessel 10. The heated coolant exits from the pressure vessel10 via conduit or hot leg 18 and is'thereafter delivered to PrimarySystem 12. I

As is well known in the art, a core assembly. including a plurality offuel rods or elements is positioned within pressure vessel 10. Alsopositioned within vessel 10, in the interest of controlling the fissionrate, are control or absorber rod assemblies; a typical such assemblybeing indicated schematically and generally at 20 and including anabsorber element 21. In accordance with the present invention. each ofthe control rod assemblies has two operative positions commensuraterespectively with full retraction and full insertion of its absorberelement into the reactor core. As shown in FIG. 1, and as will bedescribed in greater detail below, absorber element position control isachieved by providing each individual control rod assembly with ahydraulic actuator.

As may be seen from FIG. 1, and as will also be described in greaterdetail below, each independently controllable control rod assembly inaccordance with the present invention is a top actuated device whichutilizes hydraulic pressure to determine absorber element position. Thatis, the position of the absorber elements in accordance with theinvention is determined by the application of pressure to the top end ofthe hydraulic actuator which comprises part of each individual controlrod assembly. A plurality of hydraulic control lines, such as line 22-22associated with control rod assembly 20, will penetrate the pressurevessel and will deliver the control pressure which is applied to thehydraulic actuator of each control rod assembly. Each of control lines22 will have inserted therein a control valve 24. One side of each ofvalves 24 is connected to a lift pump 26 via a manifold 28. As may beseen from the flow path indicated in broken lines in FIG. 1, primarycoolant delivered to pressure vessel will flow through the individualcontrol rod assemblies and any coolant drawn off by lift pump 26 will bereturned via conduit 29 to the main coolant flow path upstream of themain circulating pump 14.

The raising of the absorber elements cannot be accomplished by the maincirculating pump 14 alone and is achieved by the opening of valves 24whereby a lift pressure differential is established across the hydraulicactuators of the control rod assemblies by the combined action of mainpump 14 and lift pump 26.

When all of the absorber elements are in the up position. as shown inthe case of control rod assembly of FIG. I, the reactor will beoperating with maximum power output. The adjustment of reactor outputpower may be accomplished in accordance with the present invention bycontrollably inserting or withdrawing individual absorber elements fromthe core.

Insertion of selected individual absorber elements into the core undernormal operating conditions is accomplished by operating valves 24 so asto remove holding pressure from the tops of the selected actuators inthe control rod assemblies. Upon the removal of the holding pressureeither gravity or the application of pressure to the top of thehydraulic actuator will cause absorber element insertion. Absorberelement insertion under emergency conditions. known as a scram, may beaccomplished either by gravity or power or a combination of both.

When power scram and/or power assisted absorber element insertion isdesired in addition to gravity insertion, communication is provided fromthe downstream side of main circulating pump 14 to the control rodassemblies via an auxiliary pump 200. Pump 200 is employed to charge anaccumulator 202 and, in the power scram embodiment, valve 24 will be athree-way valve.

It is to be noted that the supplementary flow path including pump 200,accumulator 202 and the associated check valve 204 is not necessary foroperation of the invention and the reactor and may be omitted.

Safety requirements dictate that the reactor be provided with externaldevices for indicating the position of each of the absorber elements. Inaccordance with the present invention, the position indicating devicesare preferably pressure sensitive and are responsive to the pressuredifference between the reactor vessel outlet, as measured forconvenience in the primary coolant hot leg 18, and the control line 22.One of these P position indicating devices is indicated schematically at30.

In accordance with the top actuated control techniques of the presentinvention, the forces of gravity are adequate to insure positive holddown of the absorber elements. While not necessary for operation or tocomply with safety requirements, the invention may also be provided withmeans for hydraulically assisting in the holding of the absorberelements in the down or inserted position. Thus, by including a branchconduit 32 between the cold leg 16 and the control line 22 upstream ofvalve 24, a small positive pressure acting in the down direction may beapplied to the hydraulic actuators in the control rod assemblies. Ifemployed, each of hold down lines 32 will include a flow limitingrestriction 34.

While not necessary, if deemed desirable in view of safetyconsiderations, means may be provided to prevent accidental control rodwithdrawal in the event of a rupture of the control line 22-22 betweenthe top of the control rod assembly 20 and the control valve 24. Thisadditional safety feature may take the form of a check valve 35. Checkvalve 35 may comprise a flow rate sensitive hydraulic fuse such as modelFVLl6A available from Marotta Valve Corporation of Boonton, NJ. Thecheck valve 35 or equivalent device will be installed in the controlline adjacent to the control rod assembly and will be responsive to therate of flow of coolant out of the top of the control rod assembly. Thecoolant flow rate will, of course, substantially increase in theunlikely event of a control line break. The safety valve willautomatically close when the flow rate reaches a selected level inexcess of that experienced during normal operation thereby preventinggeneration of a sufficient pressure differential to cause absorberelement withdrawal.

Referring now to FIG. 2, the pressure vessel 10, partly broken away toshow the fuel and control rod assemblies, may be seen. Pressure vessel10 includes a main vessel portion 40, the reactor top head 42 and abottom head 43. A fuel assembly 44, which includes the individual fuelrods and the absorber element guide tubes, is positioned within vessel10 below a fuel assembly alignment plate 46. An upper guide structure48, which includes the control rod assemblies, is positioned in vessel10 above fuel assembly 44 and includes an upper support plate 50 whichbridges the top of the core support barrel 52. The head 42 and the upperguide structure 48 must be removable to permit refueling of the reactorand other maintenance. Accordingly, means must be provided fordisconnecting the hydraulic control lines such as line 22 of FIG. 1.

As shown in FIG. 2, the control lines penetrate the wall of portion 40of vessel 10 via a control line penetration indicated generally at 54.Within vessel 10 the control lines are directed, in part via a controlline cluster assembly indicated generally at 56, to the tops of thecontrol rod assemblies. A control line disconnect assembly is indicatedat 58. Disconnect 58 may be of the multiple seal, single bolt connectortype which will be described in detail below in the discussion of FIGS.5 and 5A.

With reference now to FIG. 3, a control rod assembly in accordance witha first embodiment of the present invention is shown in detail. Theabsorber element 21 is positioned within a tubular extension 60 ofcontrol rod 61 which is in turn mounted within a control rod guide tube62. The guide tube, as previously noted, passes into the core assemblyand forms part of the fuel assembly 44 which also includes the fuel rodsor elements indicated generally at 64. At their lower ends the guidetubes, such as guide tube 62, are supported from the core support plate66 by means of a fuel assembly end fitting indicated generally at 68.Proper positioning of guide tubes is insured through engagement offitting 68 with fuel bundle alignment pins, such as pin 70, which aremounted from plate 66. At their opposite or upper ends the guide tubesare engaged by the fuel assembly upper end fitting 72. A tubularextension 73 of upper end fitting 72 is received in the fuel assemblyalignment plate 46. Fluid communication between guide tube 62 and ahydraulic cylinder 74 is achieved through upper end fitting 72 and plate46. The hydraulic cylinder 74 is supported by the upper guide structuresupport plate 50 and by a further upper support plate Sl. The hydrauliccylinder 74 terminates, at its upper end, in a lift buffer assembly,indicated generally at 76, which provides communication between theupper end of cylinder 74 and the control line 22'.

Guide tube 62 is provided with a coolant flow port 80. Port 80 mayeither be in the wall of tube 62 adjacent the fuel assembly lower endfitting 68 as shown or may actually be formed in pin 70 withcommunication being via the bottom of the tubular extension of fitting68. Additional flow ports 82 are provided in the tubular extension 73 ofthe fuel assembly upper end fitting 72. The upper end of the control rod61 is connected to a lift piston assembly indicated generally at 83. Ina preferred embodiment piston 83 includes a pair of spacially displaceddiscs 84 and 86. With the absorber element in the inserted positionshown in FIG. 3, the lower disc 84 is in sealing relationship with abottom seal defined by the upper end of the tubular extension 73 ofupper end fitting 72. The top seal, which is engaged by upper disc 86with the control rod in the full withdrawn position, is indicated at 88and is formed on the lift buffer assembly 76.

With reference now to FIG. 3A, which is an enlarged view of a portion ofa preferred embodiment of the control rod assembly of FIG. 3, a numberof particularly novel features of the present invention may be seen.Because of its design, the control rod assembly of the present inventionmay use commercially available tubing for hydraulic cylinder 74. Thelift piston discs 84 and 86 are loose fitting within cylinder 74 andthus have large clearances relative to the bore of the cylinder. Also,for reasons which will become apparent from the description to follow,the lift piston discs are provided with rounded edges. Use of off theshelf tubing and the ability to operate with relatively large clearancesresults in ease of manufacture of the control rod assemblies and lowcost. Also, large variations in tube ovality and straightness can betolerated and contamination such as the build up of scale on the innerwalls of cylinder 74 will not have a deleterious effect on operation.The large clearance between the lift piston and walls of cylinder 74,however, requires relatively high lift flows in order to permit raisingof the absorber elements. In accordance with the present invention,these high flows can be tolerated because they exist only during theshort time periods when a control rod withdrawal is occurring and theflow rates will decrease to a minimal value when lift piston disc 86 isseated at the top of its stroke against top seal 88.

An additional design criteria of the control rod as- ,semblies of thepresent invention requires that flow port be sufficiently large topermit adequate flow to insure the requisite cooling of the absorberelement 60. However, the size of port 80 must also be restricted so thatthe pressure differential across the reactor core will be taken acrossthe orifice rather than across the control rod; this sizing beingnecessary to prevent the core A P from shifting the absorber element.Since the size of the absorber element 60-21 and guide tube 62 are fixedby nuclear design criteria, and the size of flow port 80 is selected asnoted above, the lift piston discs 84 and 86 must be designed to achievea minimum gravity scram time. The diameter and shape of discs 84 and 86are thus adjusted to achieve this scram time. In addition, the spacingbetween discs 84 and 86 must be such that the characteristics of a highloss piston will result due to pressure recovery between the discs 84and 86. In designing the piston so as to achieve the desired scram time,it is also important to insure that the piston will have minimumcylinder wall contact areas.

FIG. 3A shows means for providing a fluid seal between the upper endfitting 72 and the fuel assembly alignment plate 46. As may be seen inFIG. 3A, a sleeve 300 is pinned to and positioned about the tubularextension 73 of upper end fitting 72; sleeve 300 being slidably mountedby pins 302 which engage slots in sleeve 73. Sleeve 300 is provided witha convex, and preferably spherical, shoulder 304 which cooperates with aconical enlargement 306 of the aperture in plate 46. In accordance withone embodiment of the invention, the spherical valve element defined byshoulder 304 on sleeve 300 is urged into sealing relationship with theseat defined by the conical surface 306 on plate 46 by means of aloading spring 308. The design of the surfaces 304 and 306 will resultin a line of contact or seal and will insure sealing even if there issome slight rotation or misalignment between the various components. Theloading spring 308 serves the additional function of holding down thefuel assembly.

The cooperation between surfaces 304 of sleeve 300 and surface 306 ofplate 46 as well as the seal between the lower disc 84 of piston and asealing surface at the top of extension 73 of upper end fitting 72prevents downward flow of coolant from the interior of the cylinder 74with the absorber element in the inserted position shown in FIG. 3A. Thevalve seat 310 preferably has the shape of a segment of a cone andcooperates with the exterior spherical surface on the disc 84 to providea line of contact seal which will be maintained even if there is slightrotation or canting of the lift piston assembly.

It should also be noted that a mechanical buffer element may be providedbetween the top of extension 300 and piston 84. Thus, for example, aspring may be installed about the piston shaft 312 which connects thepiston assembly to the control rod 61. In a typical example, the springwould be seated against a shoulder on shaft 312 at its upper end and toa sealing plate at its lower end. The piston shaft 312 would passthrough the sealing plate and would be movable with respect thereto. Thesealing plate would have, at its lower side, a surface which wouldcooperate with the sealing surface 310 on sleeve 300. In such aconfiguration the internal sealing would, accordingly, not be achievedby means of direct cooperation between disc 84 and the upper end fitting72. The spring if employed, would be compressed in decelerating thecontrol rod during a scram only and during such deceleration the pistonshaft 312 would slide through the sealing plate.

With reference to FIG. 38, details of the piston extension which formspart of the control rod top buffer 76 is shown. The piston extensioncomprises a flow restrictor having multiple tapers such as shown at 314,315 and 316. The first or outwardly disposed taper performs only amechanical lead-in function. The tapered sections 315 and 316 betweenthe mechanical lead-in portion 314 and the upper disc 86 of piston 85are designed in the manner to be described below. It is to be noted thatthe top buffer assembly, in cooperation with the flow restricting pistonextension, prevents mechanical impact and water hammer pulsations byproviding flow reduction which causes deceleration of the control rod insuch a manner that flow through control line 22 is substantially shutoff prior to the seating of disc 86 against seat 88. The seat 88, asnoted, is a conical segment which mates with the spherical surface ondisc 86 to define a line of contact with the valve closed. The use of aconical seat and cooperating spherical valve element, as also previouslynoted, permits angular misalignment while still providing an adequateseal. It is understood that either disc 86 or the tapered portion of theplug on the seat 88 may be permitted to float freely between stops onpiston 85 in the interest of improving seating in the presence ofmisalignments.

In the interest of promoting positive seating the flow should be reducedprior to seating and, as noted above, the dynamic lift forces must beconverted to static holding forces in such a manner as to prevent waterhammer pulsations from developing. These criteria are satisfied by thetapered piston design of the present invention. In designing the plug orpiston extension, it is necessary that a maximum size or cross-sectionalarea be selected so that the minimum force which guarantees seating ofthe piston is developed. The length and shape of the taper or tapers arethus selected so that the flow reduction and the dynamic to static forcetransition take place in such a manner and in such a time interval so asto provide a stable condition which minimizes the impact forces and thepressure pulsations generated as a result of the flow shut off. Theforces in question are. of course, the summation of the force developedacross piston 85 and also the force developed across the section of thepiston extension which is within the throat 318 of buffer 76. Inaccordance with a preferred embodiment of the invention, the plug is ofconical shape and tapers in stepwise fashion from a maximum diameteradjacent disc 86 to a minimum diameter at the junction of sections 314and 315 in accordance with the above noted criteria. It is to be notedthat the shape of the plug may be irregular in order to obtain thedesired characteristics of movement of the absorber element during thedeceleration portion of the control rod withdrawal stroke. Otherdeceleration means, and particularly mechanical energy absorbingdevices, can be mounted on the control rod assembly to provide smoothrod seating if desired.

Considering operation of the control rod actuator of FIG. 3, coolantwill normally enter guide tube 62 through flow port and will exitthrough the flow ports 82. As discussed above, due to the sizing of port80, the pressure of the coolant on the lower end of tubular housing 60for absorber element 21 will be insufficient by itself to overcome theforces of gravity and raise the control rod assembly. However, ifreactor design criteria so requires, other means can be employed toprovide a greater margin against the coolant pressure raising theabsorber element. Thus, as briefly noted above, if considered desirablean additional holddown hydraulic pressure may be applied against the topsurface of piston 84 via line 32 in the manner described above in thediscussion of FIG. 1. When it is desired to raise the absorber element,communication between the upper end of cylinder 74 and lift pump 26 isestablished via valve 24 and the pressure differential across liftpiston will increase thus unseating disc 84 from seat 310. Once thepiston has been unseated, coolant will flow into cylinder 74 throughports 80 and 82 and the pressure differential across the piston willcause the absorber element to continue to move upwardly until disc 86becomes seated against seat 88.

In accordance with a preferred embodiment, the pressure of the coolantwhich enters cylinder 74 via ports 80 and 82 will be sufficient to holdthe absorber element and its associated hydraulic actuator assembly inthe raised position; the down stream pressure being maintained by liftpump 26 and main pump 14 acting together. However, if necessary ordesired, lift pump 26 may be intermittently operated and the pressureprovided by main pump 14 alone may be utilized to maintain the controlrod assembly in the up position. When it is desired to reinsert theabsorber element under normal operating conditions, valve 24 will beoperated in such a manner as to allow the pressure in cylinder 74 toequalize around disc 86. After the pressure has equalized, gravity willcause insertion of the absorber element. During insertion, fluid will bedisplaced from guide tube 62 via port 80 and by flow upwards in theannulus between control rod 61 and the guide tube 62. Fluid which fillscylinder 74 during insertion enters ports 82 and bypasses discs 84 and86 until such time as disc 84 becomes seated on the top of tubularextension 73 of upper end fitting 72. As noted above in the discussionof FIG. 1, valve 24 may be a three-way valve so as to permit theapplication of positive pressure to piston 85 so as to assist the forcesof gravity during absorber element insertion.

The FIG. 3 embodiment does not show a separate scram buffer which isemployed to decelerate the control rod assembly at the bottom of thedown stroke. Scram buffers are generally employed and may take the fonnof hydromechanical devices located on the top end of tubular extension73 of upper end fitting 72 or hydraulic devices positioned within guidetube 62 below port 80.

A first control line penetration technique in accordance with thepresent invention is shown in FIG. 4. A preferred embodiment of acontrol line disconnect mechanism for use with the penetration techniqueof FIG. 4 is shown in FIGS. 5 and 5A. The penetration technique of FIG.4 includes an aperture in the wall of pressure vessel portion 40; theaperture being provided with a build up of stainless steel 90. Thecontrol lines, such as line 22, pass through the aperture and terminateinternally of a multi-apertured plug 92. The external control lines ortubes 22 are brazed, welded or mechanically joined to plug 92 and theplug is seal welded to the inner wall of the pressure vessel whereby aliquid-gas separation between th interior of the vessel and theatmosphere is provided. Plug 92 may be comprised of matching plates withthe outer plate being welded to the vessel and the plates thereafterbeing mechanically held together to form an assembly similar to thedisconnect device to be described below in the discussion of FIG. 5. Itis to be noted that the location of the vessel side wall penetration ispreferably above the primary nozzle through which coolant is deliveredto the interior of the vessel. This location of the penetration isdepicted in FIGS. 1 and 8.

After penetrating the pressure vessel wall, the internal control lines22' are directed upwardly toward the junction of head 42 and the mainvessel portion 40. The control lines are routed within the control linecluster assembly 56 which includes an inner tube shroud 94. Shroud 94protects the tubular control lines from cross flow and vibration whichwould otherwise result from direct impingement of the coolant thereon.The control line cluster assembly is positioned between the inner wallof vessel portion 40 and the core support barrel 52. At the top ofshroud 94 the control line cluster assembly is provided with a multipleseal, single bolt connector 58. The control line coupling portions ofconnector 58 are located in an aperture provided therefor in the upperguide structure support plate 50 and it is to be noted that a sealingring 96 is provided between plate 50 and the core support barrel 52 toprevent leakage of coolant past connector 50 and up into the vessel head42. A pin 98 locates shroud 94 relative to the vessel and takes uprestraining torque during assembly and disassembly. Pin 98 engages anaperture in an internal flange 99 provided on pressure vessel portion40.

With reference now to FIG. 5, an enlarged crosssectional view ofmultiple seal single bolt connector 58 is shown. Connector 58 includes alower flange 100, an upper flange 102 and, positioned therebetween, amultiple seal plate 104. The multiple seal plate 104 will typicallycomprise a compressible metal plate assembly which is keyed intoposition, by a key 106 formed integral with flange 100, whereby theapertures therein are aligned with the passages defined by the alignedholes in the upper and lower flanges 102 and 100. The internal controllines 22 and the control line segments 22", which extend between plug 92and connector 58, are brazed or otherwise connected in sealingrelationship to apertures in respective flanges 102 and 100 as shownwhereby the disconnect assembly functions as a portion of a plurality ofcontrol lines when in the assembled position. An enlarged perspectiveview of the lower flange 100 is shown in FIG. 5A. The details of the key106 are clearly shown in FIG. 5A. The configuration of key 106 is suchthat, upon disconnecting the control lines, the seal 104 will remain inposition on lower flange 100.

Upper flange 102 of connector 58 is provided with one or more torquelugs 108 which are keyed into the upper guide plate 50 to both locatethe connector assembly 58 and also to prevent turning of flange 102during assembly and disassembly operations. Flange 102 thus is seated ina pilot hole in upper guide structure support plate 50 and will come offwith plate 50 during a disassembly operation. With connector 58 in theassembled position, the upper and lower flanges are held together by astud 110 and a retainer nut 112. The stud 110 is threadably engaged inthe lower flange 100 and, in turn, is engaged by the retainer nut 112which is tightened down against an internal flange provided at the topof the main body portion of upper flange 102. The upper flange 102 isalso provided with a tubular extension 114 which functions as a toolguide during assembly and disassembly operations. A tool inserted inextension 114 will be directed into the hexagonal recess provided in theupper end of retainer nut 112 whereby the retainer nut may be removedand the upper flange 102 thereafter separated from the seal plate 104and lower flange 100 when the upper guide structure support plate 50 isremoved.

It is to be noted that the single bolt connector 58 is also providedwith a spring loaded locking device which comprises locking member 116and associated spring 118. A pin 119 on locking member 116 engages agroove at the top of retainer nut 112 whereby the locking deviceprevents rotation of nut 112 as could otherwise result from vibrationsencountered during normal reactor operation. The tool used to remove andtighten retainer nut 112 is configured so as to push locking member 116outwardly to thereby disengage pin 119 from the cooperating groove innut 112 when the tool is inserted.

FIGS. 6 and 7 respectively depict an alternate pressure vesselpenetration technique and a second embodiment of a disconnect mechanismin accordance with the present invention. It is to be noted, however,that the disconnect mechanism of FIG. 5 may be employed with thepenetration technique of FIG. 6 and the disconnect mechanism shown indetail in FIG. 7 may be employed with the penetration technique of FIG.4. The penetration scheme of FIG. 6 differs from that of FIG. 4primarily in the fact that the control lines 22 are continuous wherethey pass through the wall of the main portion 40 of the pressurevessel. In the FIG. 4 embodiment the tubes defining the control lineswere broken at the plug 92 whereby the plug defined the high pressureboundary or liquid-gas interface. Thus in the FIG. 4 embodiment,apertures in the plug defined fluid flow paths between the control lineportions which were located at atmospheric pressure externally of thepressure vessel and the control line segments internally of the vesseland exposed to the pressurized coolant. In the FIG. 7 embodiment thecontrol lines will be brought to the apertured pressure vessel wall inthe' form of a bundle of tubes and the tube bundle will'be supported atthe wall by means of a flange 120 which is welded to the external wallof the pressure vessel. The flange 120 is also welded to an externalprotective shroud 122 which supports and guides the tube bundle to anintegral, apertured, external flange 123. In the FIG. 7 embodiment theprimary seal is provided by joining, by suitable means, the internaltubes 22" and the external tubes 22 to flange 123 whereby the tubes onthe vessel side of the flange will be exposed to the pressurized coolantand the tubes to the other side of flange 123 are exposed to theatmosphere. Alternatively, the hydraulic control lines may be broughtout through the walls of shroud 122 and the end of the shroud would beprovided with a plug rather than apertured flange 123.

Although not shown in FIG. 6, an inner tube shroud, such as shroud 94 ofFIG. 4, will also be provided and will extend between the inner wall ofthe pressure vessel adjacent the penetration up to a support plate 124.The spring loaded disconnect mechanism of FIG. 7 will be positionedabove support plate 124 and will be described in detail below. Above thedisconnect mechanism the control line continuations 22 will passupwardly through the flange at the top of the core support barrel 52 andalso through the upper guide structure support plate 50 as shown.

Referring now to FIG. 7, it may be seen that the disconnect mechanism ofFIGS. 6 and 7 includes spring loaded devices which couple eachindividual control line 22 to an associated control line extension 22.The coupling mechanism in each case includes a retainer 126 permanentlyattached to each of the control lines beneath support plate 124. Eachcoupling mechanism also includes a spring 128 and a tube seal 130. Thelower ends of the control line extensions 22 are provided with an outertaper and the upper ends of the tube seals 130 are provided with acomplementary internal taper; the tapered surfaces providing sealingcontact between the tubular control line extensions and tube seals. Theupper end of each vessel penetrating control line 22 is received in asocket provided therefor at the bottom of a tube seal 130 and thecontrol lines are brazed to the tube seals thereby providing leak tightpermanent connections. It will be observed that each control line, suchas line 22 of FIG. 7, passes through support plate 124 and is movableaxially with respect thereto. The springs 128 load the seals 130 againstthe control line extensions which extend downwardly through the coresupport barrel flange and the upper guide structure flange as shown.

During a refueling operation, the pressure vessel head 42 will beremoved and the upper guide structure will thereafter be lifted out ofthe pressure vessel. Upon upper guide structure removal the disconnectmechanisms of FIG. 7 will automatically separate the control lines and.after refueling. the control lines will be automatically reconnectedmerely by insuring proper alignment as the upper guide structure isrepositioned with its supporting flange on the internal pressure vesselsupporting shoulder 99. In accordance with side penetration techniquesof the present invention, the location of the disconnect mechanism belowflange 99 permits the reactor internals; i.e., the core barrel and core;to be removed for inspection and maintenance.

FIG. 8 depicts a third embodiment of a pressure vessel penetrationtechnique in accordance with the present invention. In the FIG. 8approach a ring known as a dutchman is positioned between the top of themain pressure vessel portion 40 and the head 42. The dutchman isindicated at 140 in FIG. 8. When the dutchman approach is employed it isunnecessary to provide for a disconnect mechanism or mechanismsinternally of the pressure vessel. Rather, each of the control lineswill be severed, typically by the use of standard connectors. externallyof the pressure vessel and the dutchman and upper guide structure willbe removed from the pressure vessel together.

The penetration technique of FIG. 8 also includes a pair of primarypressure seals 142 and 144 which respectively provide a fluid tight sealbetween dutchman and head 42 and between the dutchman and the mainpressure vessel portion 40. The dutchman is held in position by aplurality of closure bolts, not shown, which extend downwardly from anexternal flange 146 on head 42 through the dutchman and into the top ofmain vessel portion 40. The control lines 22 will be dispersed about theperiphery of the vessel so as to pass through dutchman 140 withoutinterference with the closure bolts.

FIG. 8 also shows the primary nozzle 148 through which the coolant isdelivered to the vessel. As noted above. the control line penetrationwill preferably, in the interest of isolating the lines from unduestresses caused by the relatively large volume of primary coolant flow,be located above nozzle 148.

FIG. 9 shows a fourth reactor vessel penetration technique in accordancewith the present invention. In the FIG. 9 embodiment the control linesenter the pressure vessel through the vessel top head 42. In order topermit penetration, the head is provided with an aperture which receivesa multiple seal assembly which is similar to the disconnect assembly 58of FIG. 5. That is, the vessel penetration of FIG. 9 includes an upperflange member 150 and a lower flange member 152. Both of the upper andlower flange members are provided with a number of aperturescommensurate with the number of control lines and the flanges areseparated by an apertured multiple seal plate 154; the apertures in theupper and lower flanges and the seal plate being in registration withthe penetration apparatus assembled as shown. The penetration apparatusis mounted above on a flange support assembly 156 located internally ofthe pressure vessel. Assembly 156 is in turn supported on the uppersupport plate 50. The lower flange 152 is supported from head 42 bymeans of seal bolts 158 and is held tightly against the head thusproviding. through the use of a compressible seal 160, a fluid tightconnection. Upper flange 150 is bolted to lower flange 152 by means ofseal bolts 162 whereby the multiple seal plate 154 is compressed betweenthe flanges. Externally of the pressure vessel the control lines, suchas line 22, are protected by a shroud 164 and the individual controllines are terminated within the upper flange 150 to which they arebrazed or otherwise attached by means which provide a fluid tightconnection. Fluid communication between the ends of the external controllines located within the upper flange 150 and the internal controllines, such as line 22, is provided by the upper flange, the seal plate154 and a portion of the apertures in the lower flange 152. The internalcontrol line extensions 22' are brazed or otherwise connected in a fluidtype manner to the appropriate apertures in flange 152. Accordingly,continuous and leak-proof control lines are provided from the controlvalves located externally of the pressure vessel through the wall of thevessel to the hydraulic cylinders 74 of the control rod actuators. Theproper alignment between the upper and lower flanges and the multipleseal plate 154 is achieved by means of bolts 162 and alignment betweenthe flange support assembly 156 and the core barrel 52 and the upperguide structure support plate 50 is achieved by means of alignment keys166. 7

It is to be observed that a penetration scheme similar to that shown inFIG. 9 may be employed in the top actuated control system of the presentinvention wherein the control lines enter the pressure vessel throughthe bottom thereof. In the case of bottom penetration, however, theupper flange member 150 is omitted and apertures are provided in thepressure vessel bottom head 43 itself.

FIG. depicts a fuel bundle hold down technique in accordance with thepresent invention. As is well known, in view of the upwardly directedpressure exerted by the large volume of coolant circulated through thecore and also because of the vibrations encountered during operation,means are needed to positively hold down the fuel elements which aremounted below the fuel assembly alignment plate 46. In accordance withthe invention, means for holding down the fuel elements may, with theexception of the pistons and associated hydraulic circuitry, besubstantially the same as the apparatus for controlling the position ofthe absorber elements. Thus, the hydraulic cylinder 74 may be allowed tofloat freely between a pair of stops defined by external flanges l7()and 172 respectively positioned at and adjacent to the upper end of.cylinder 74. The lower end of cylinder 74 may be provided with an innertaper which is complementary to an outer taper on the upper end ofextension 73 of upper end fitting 72. Regardless of whether scaling isdesired, the lower end of cylinder 74 will be urged against the upperend fitting extension. When the apparatus of FIG. 10 is used for fuelelement hold down purposes, there will typically be five devicesemployed to hold down each individual fuel element bundle which may, forexample, comprise 250 or more individual tubes which contain the pelletsof fissionable material which comprise the fuel. The cylinder 74, whichas noted is free floating, is positioned within an upper guide structuresupport tube 174. Tube 174 is a load bearing element extending betweenand being joined to fuel assembly alignment plate 46 and upper guidestructure support plate 50. The weight of cylinder 74 will typically beselected so that the fuel hold down may be accomplished solely byreliance upon gravity. However, if deemed desirable, a spring 176 may beinserted between plate 51 and the lower flange 172 so as to assist inmechanical hold down. When the apparatus is used for fuel assembly holddown purposes, the tops of cylinder 74 will be sealed. If used forcontrol purposes, the tops of the cylinders would be formed as shown inFIG. 3B and a hydraulic piston assembly will be located within thecylinder.

The apparatus of FIG. 10 may also be employed with the prior art type ofganged control rod assembly. In a ganged rod arrangement, however, thetube 174 and cylinder 74 would be slit.

While preferred embodiments have been described, various modificationsand substitutions can be made without departing from the spirit andscope of the present invention. Accordingly, this invention has beendescribed by way of illustration and not limitation.

We claim:

I. In a nuclear reactor, the reactor having a fuel as sembly includingfissionable fuel elements and neutron absorber elements movable withrespect to the fuel elements, the fuel assembly and fluid responsiveactuators for positioning the absorber elements being positioned withina pressure vessel, the actuators including piston means coupled to theabsorber elements, the pressure vessel having a main portion and aremovable head, the improvement comprising:

a first plurality of conduits commensurate in number with all of theabsorber element actuators present in the reactor, said first pluralityof conduits being located externally of the pressure vessel and havingfluidic actuator position control signals applied to first ends thereof,the second ends of said conduits of said first plurality being formedinto a bundle of tubular members closely positioned to one another;

a second plurality of conduits commensurate in number with said firstplurality of conduits, said second plurality of conduits being locatedinternally of the pressure vessel and having first ends coupled torespective absorber element actuators, the second ends of said conduitsof said second plurality being formed into a bundle of tubular membersclosely positioned to one another; and means for coupling the secondends of each of said first plurality of conduits to the second ends ofrespective of said second plurality of conduits, said coupling meanspassing through the wall of the pressure vessel main portion anddefining a liquidgas separation between the interior and exterior of thepressure vessel whereby absorber element position control signalsgenerated externally of the pressure vessel may be applied to the fluidresponsive actuators at one side only of the actuator pistons, saidcoupling means being associated with an aperture in the pressure vesselmain portion wall and comprising: plug means sealed to the pressurevessel main portion wall about the periphery of the aperture therein,said plug means having a plurality of passages therethrough, the secondends of said conduits of said first plurality being terminated inrespective of said plug means passages adjacent the exterior sidethereof;

connector means positioned internally of the pressure vessel, saidconnector means having a plurality of passages therethrough, said secondends of the second plurality of conduits being connected to respectiveof said connector means passages; and

a third plurality of conduits extending between the pressure vessel sideof said plug means and said connector means, said third plurality ofconduits being terminated at first ends in respective of said plug meanspassages whereby said plug means provides continuous communicationbetween the individual conduits of said first and third pluralities, thesecond ends of said conduits of said third plurality being coupled tothe second ends of respective of said second plurality of conduits byrespective passages in said connector means.

2. The apparatus of claim 1 wherein the reactor fuel assembly ispositioned within a core barrel, the core barrel being removablysupported within and spacially displaced from the pressure vessel, andwherein said connector means and plug means are vertically displaced andsaid third plurality of conduits is located in the space between thecore barrel and pressure vessel.

3. The apparatus of claim 2 further comprising:

shroud means surrounding and protecting said third plurality ofconduits.

4. The apparatus of claim 1 further comprising:

shroud means surrounding and protecting said third plurality ofconduits.

5. The apparatus of claim 1 wherein said connector means comprises:

multiple seal disconnect means for simultaneously interrupting andreestablishing communication between the conduits of said second andthird pluralities.

6. The apparatus of claim 3 wherein said connector means comprises:

multiple seal disconnect means for simultaneously interrupting andreestablishing communication between the conduits of said second andthird pluralities.

7. The apparatus of claim 1 wherein a liquid coolant is circulatedthrough the reactor pressure vessel and nozzle means is provided in thepressure wall for discharging the coolant into the pressure vessel, saidcoupling means being positioned above the coolant discharge nozzle meanswhereby said coupling means is disposed in a location which is out ofthe main reactor coolant flow path.

8. The apparatus of claim 3 wherein a liquid coolant is circulatedthrough the reactor pressure vessel and nozzle means is provided in thepressure wall for discharging the coolant into the pressure vessel, saidcoupling means being positioned above the coolant discharge nozzle meanswhereby said coupling means is disposed in a location which is out ofthe main reactor coolant flow path.

9. The apparatus of claim 6 wherein a liquid coolant is circulatedthrough the reactor pressure vessel and nozzle means is provided in thepressure wall for discharging the coolant into the pressure vessel, saidcoupling means being positioned above the coolant discharge nozzle meanswhereby said coupling means is disposed in a location which is out ofthe main reactor coolant flow path.

10. The apparatus of claim 2 wherein said connector means is positionedabove said plug means and substantially at the level of the junction ofthe pressure vessel head and body portions whereby said connector meansis accessible with the pressure vessel head removed.

11. The apparatus of claim 6 wherein said multiple seal disconnect meansis positioned above said plug means and substantially at the level ofthe junction of the pressure vessel head and body portions whereby saidmultiple seal disconnect means is accessible with the pressure vesselhead removed.

12. The apparatus of claim 9 whereby said multiple seal disconnect meansis positioned above said plug means and substantially at the level ofthe junction of the pressure vessel head and body portions whereby saidmultiple seal disconnect means is accessible with the pressure vesselhead removed.

13. The apparatus of claim 5 wherein said disconnect means comprises:

movable seal means, said seal means being permanently connected to thesecond ends of the conduits of said third plurality and releasablyengaging the second ends of the conduits of said second plurality;

means for resiliently urging said seal means into leak proof engagementwith the conduits of said second plurality; and

means limiting the movement of said seal means whereby the conduits ofsaid second plurality may be withdrawn from said seal means upon removalof the reactor core barrel.

14. The apparatus of claim 9 wherein said disconnect means comprises:

movable seal means, said seal means being permanently connected to thesecond ends of the conduits of said third plurality and releasablyengaging the second ends of the conduits of said second plurality.

means for resiliently urging said seal means into leak proof engagementwith the conduits of said second plurality; and

means limiting the movement of said seal means whereby the conduits ofsaid second plurality may be withdrawn from said seal means upon removalof the reactor core barrel.

1. In a nuclear reactor, the reactor having a fuel assembly includingfissionable fuel elements and neutron absorber elements movable withrespect to the fuel elements, the fuel assembly and fluid responsiveactuators for positioning the absorber elements being positioned withina pressure vessel, the actuators including piston means coupled to theabsorber elements, the pressure vessel having a main portion and aremovable head, the improvement comprising: a first plurality ofconduits commensurate in number with all of the absorber elementactuators present in the reactor, said first plurality of conduits beinglocated externally of the pressure vessel and having fluidic actuatorposition control signals applied to first ends thereof, the second endsof said conduits of said first plurality being formed into a bundle oftubular members closely positioned to one another; a second plurality ofconduits commensurate in number with said first plurality of conduits,said second plurality of conduits being located internally of thepressure vessel and having first ends coupled to respective absorberelement actuators, the second ends of said conduits of said secondplurality being formed into a bundle of tubular members closelypositioned to one another; and means for coupling the second ends ofeach of said first plurality of conduits to the second ends ofrespective of said second plurality of conduits, said coupling meanspassing through the wall of the pressure vessel main portion anddefining a liquid-gas separation between the interior and exterior ofthe pressure vessel whereby absorber element position control signalsgenerated externally of the pressure vessel may be applied to the fluidresponsive actuators at one side only of the actuator pistons, saidcoupling means being associated with an aperture in the pressure vesselmain portion wall and comprising: plug means sealed to the pressurevessel main portion wall about the periphery of the aperture therein,said plug means having a plurality of passages therethrough, the secondends of sAid conduits of said first plurality being terminated inrespective of said plug means passages adjacent the exterior sidethereof; connector means positioned internally of the pressure vessel,said connector means having a plurality of passages therethrough, saidsecond ends of the second plurality of conduits being connected torespective of said connector means passages; and a third plurality ofconduits extending between the pressure vessel side of said plug meansand said connector means, said third plurality of conduits beingterminated at first ends in respective of said plug means passageswhereby said plug means provides continuous communication between theindividual conduits of said first and third pluralities, the second endsof said conduits of said third plurality being coupled to the secondends of respective of said second plurality of conduits by respectivepassages in said connector means.
 2. The apparatus of claim 1 whereinthe reactor fuel assembly is positioned within a core barrel, the corebarrel being removably supported within and spacially displaced from thepressure vessel, and wherein said connector means and plug means arevertically displaced and said third plurality of conduits is located inthe space between the core barrel and pressure vessel.
 3. The apparatusof claim 2 further comprising: shroud means surrounding and protectingsaid third plurality of conduits.
 4. The apparatus of claim 1 furthercomprising: shroud means surrounding and protecting said third pluralityof conduits.
 5. The apparatus of claim 1 wherein said connector meanscomprises: multiple seal disconnect means for simultaneouslyinterrupting and reestablishing communication between the conduits ofsaid second and third pluralities.
 6. The apparatus of claim 3 whereinsaid connector means comprises: multiple seal disconnect means forsimultaneously interrupting and reestablishing communication between theconduits of said second and third pluralities.
 7. The apparatus of claim1 wherein a liquid coolant is circulated through the reactor pressurevessel and nozzle means is provided in the pressure wall for dischargingthe coolant into the pressure vessel, said coupling means beingpositioned above the coolant discharge nozzle means whereby saidcoupling means is disposed in a location which is out of the mainreactor coolant flow path.
 8. The apparatus of claim 3 wherein a liquidcoolant is circulated through the reactor pressure vessel and nozzlemeans is provided in the pressure wall for discharging the coolant intothe pressure vessel, said coupling means being positioned above thecoolant discharge nozzle means whereby said coupling means is disposedin a location which is out of the main reactor coolant flow path.
 9. Theapparatus of claim 6 wherein a liquid coolant is circulated through thereactor pressure vessel and nozzle means is provided in the pressurewall for discharging the coolant into the pressure vessel, said couplingmeans being positioned above the coolant discharge nozzle means wherebysaid coupling means is disposed in a location which is out of the mainreactor coolant flow path.
 10. The apparatus of claim 2 wherein saidconnector means is positioned above said plug means and substantially atthe level of the junction of the pressure vessel head and body portionswhereby said connector means is accessible with the pressure vessel headremoved.
 11. The apparatus of claim 6 wherein said multiple sealdisconnect means is positioned above said plug means and substantiallyat the level of the junction of the pressure vessel head and bodyportions whereby said multiple seal disconnect means is accessible withthe pressure vessel head removed.
 12. The apparatus of claim 9 wherebysaid multiple seal disconnect means is positioned above said plug meansand substantially at the level of the junction of the pressure vesselhead and body portions whereby said multiple seal disconnect means isaccessiblE with the pressure vessel head removed.
 13. The apparatus ofclaim 5 wherein said disconnect means comprises: movable seal means,said seal means being permanently connected to the second ends of theconduits of said third plurality and releasably engaging the second endsof the conduits of said second plurality; means for resiliently urgingsaid seal means into leak proof engagement with the conduits of saidsecond plurality; and means limiting the movement of said seal meanswhereby the conduits of said second plurality may be withdrawn from saidseal means upon removal of the reactor core barrel.
 14. The apparatus ofclaim 9 wherein said disconnect means comprises: movable seal means,said seal means being permanently connected to the second ends of theconduits of said third plurality and releasably engaging the second endsof the conduits of said second plurality. means for resiliently urgingsaid seal means into leak proof engagement with the conduits of saidsecond plurality; and means limiting the movement of said seal meanswhereby the conduits of said second plurality may be withdrawn from saidseal means upon removal of the reactor core barrel.